Date & Time anomaly

[tom bonacci]

Greetings:

My PB2400 seems to be recording incorrect dates/times for the
modification dates on files.  The "Date & Time" control panel reads the
correct time but if I copy a recently modified file from another Mac to
the PB it shows up on the PB with something odd like 7-Feb-1975.

Question:  Is this a symptom of the lithium clock battery having died? 
If so, what type of battery is required, where is it, and how difficult
is it to replace?

thanks,
-tom